1. Field of the Invention
The present invention relates to a medical image processing technology for representing a characteristic of a tubular structure in a three-dimensional medical image.
2. Description of the Related Art
Medical image analysis techniques have been advancing rapidly with a wide spread use of multi-detector row computed tomography in clinical practice. For example, in the field of cardiac medicine, it has become possible to image the entire heart in a shorter period of time and obtain an image without substantially any artifact due to cardiac motion. Consequently, in the image diagnosis of cardiac region, more detailed diagnosis of a stenosis portion of a coronary artery has become possible. In the field of coronary artery observation, a method for specifying a center line of an observation target coronary artery and examining orthogonal cross-sections orthogonal to the center line along the center line and a method for examining an image representing a cross-section along the center line of the blood vessel using a CPR (Curved Planar Reformation) technique as described, for example, in Japanese Unexamined Patent Publication No. 2009-195561 are generally known. Here, the doctor examines as to what type of stenosis is present at which position of the blood vessel. Blood vessel can be clogged by a hard plaque in which the blood vessel is clogged by a completely calcified area or by a soft plaque in which the blood vessel is clogged by a soft tissue, such as fat. In CT images, the former can be discriminated as having a signal higher than the CT value of a normal blood vessel lumen and the latter can be discriminated as having a signal lower than the CT value of a normal blood vessel lumen.
When a specific plaque is discovered as a result of such blood vessel observation, the doctor needs to observe a three-dimensional plaque distribution adjacent to the plaque. In such a case, if an orthogonal cross-section image of the blood vessel is the observation target, it is necessary to perform observation by moving the position of orthogonal cross-section back and forth along the center line of the blood vessel. In the mean time, if a CPR image of the blood vessel is the observation target, it is necessary to perform observation by rotating the cross-section with the center line as the rotational axis.
That is, in the orthogonal cross-section image of the blood vessel, it is possible to know the plaque distribution and state of stenosis in all circumferential directions of the blood vessel at the position of the orthogonal cross-section, but it is difficult to observe how the plaque presents in the depth direction along the center line of the blood vessel and how the blood vessel is narrowed. In the CPR image of the blood vessel, it is possible to know the plaque distribution and state of stenosis in the depth direction along the center line of the blood vessel, but these are the states in a particular cross-section along the center line of the blood vessel and it is impossible to observe how the plaque is distributed and how the blood vessel is narrowed over the entire circumference of the blood vessel.
The present invention has been developed in view of the circumstances described above, and it is an object of the present invention to provide a medical image processing apparatus, method and program capable of obviously visualizing a characteristic of a tubular structure in a three-dimensional image.